Guard interval signaling for data symbol number determination

ABSTRACT

Certain aspects of the present disclosure generally relate to wireless communications and, more particularly, to techniques for accurately determining a number of data symbols in a data packet. The techniques provided herein may allow a receiving terminal to correct number of symbol calculations based on such ambiguous length field values.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional PatentApplication Ser. No. 13/221,604 entitled, “GUARD INTERVAL SIGNALING FORDATA SYMBOL NUMBER DETERMINATION”, filed Aug. 30, 2011, which claimsbenefit of U.S. Provisional Patent Application Ser. No. 61/378,642,filed Aug. 31, 2010, each of which is herein incorporated by reference.

BACKGROUND

1. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to techniques for accuratelydetermining a number of data symbols in a data packet.

2. Background

In order to address the issue of increasing bandwidth requirementsdemanded for wireless communications systems, different schemes arebeing developed to allow multiple user terminals to communicate with asingle access point by sharing the channel resources while achievinghigh data throughputs. Multiple Input Multiple Output (MIMO) technologyrepresents one such approach that has recently emerged as a populartechnique for next generation communication systems. MIMO technology hasbeen adopted in several emerging wireless communications standards suchas the Institute of Electrical and Electronics Engineers (IEEE) 802.11standard. The IEEE 802.11 denotes a set of Wireless Local Area Network(WLAN) air interface standards developed by the IEEE 802.11 committeefor short-range communications (e.g., tens of meters to a few hundredmeters).

A MIMO system employs multiple (N_(T)) transmit antennas and multiple(N_(R)) receive antennas for data transmission. A MIMO channel formed bythe N_(T) transmit and N_(R) receive antennas may be decomposed intoN_(s) independent channels, which are also referred to as spatialchannels, where N_(S)≦min {N_(T), N_(R)}. Each of the N_(S) independentchannels corresponds to a dimension. The MIMO system can provideimproved performance (e.g., higher throughput and/or greaterreliability) if the additional dimensionalities created by the multipletransmit and receive antennas are utilized.

In wireless networks with a single Access Point (AP) and multiple userstations (STAs), concurrent transmissions may occur on multiple channelstoward different stations, both in the uplink and downlink direction.Many challenges are present in such systems.

SUMMARY

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes generating a data packetcomprising one or more data symbols, providing, in a preamble field ofthe data packet, a length field that may be used to calculate a numberof symbols by a receiving entity, as well as correction field theprovides an indication of whether or not the calculated number ofsymbols should be corrected, and transmitting the data packet.

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes receiving a data packetcomprising one or more data symbols, extracting a length field and acorrection field from the data packet, and calculating a number of datasymbols in the packet, based on the length field and the correctionfield.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forgenerating a data packet comprising one or more data symbols, means forproviding, in a preamble field of the data packet, a length field thatmay be used to calculate a number of symbols by a receiving entity, aswell as correction field the provides an indication of whether or notthe calculated number of symbols should be corrected, and means fortransmitting the data packet.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forreceiving a data packet comprising one or more data symbols, means forextracting a length field and a correction field from the data packet,and means for calculating a number of data symbols in the packet, basedon the length field and the correction field.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes at least oneprocessor configured to generate a data packet comprising one or moredata symbols, provide, providing, in a preamble field of the datapacket, a length field that may be used to calculate a number of datasymbols by a receiving entity and a correction field that indicateswhether or not the calculated number of symbols should be corrected, andtransmit he data packet and a receiving entity may calculate a number ofdata symbols based on the Length field and the correction field; and amemory coupled with the at least one processor.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes at least oneprocessor configured to receive a data packet comprising one or moredata symbols, extract a length field and a correction field from thedata packet, and calculate a number of data symbols in the packet, basedon the length field and the correction field; and a memory coupled withthe at least one processor.

Certain aspects of the present disclosure provide a computer-programproduct comprising a computer-readable medium having instructions storedthereon. The instructions are generally executable by one or moreprocessors for generating a data packet comprising one or more datasymbols, providing, in a preamble field of the data packet, a lengthfield that may be used to calculate a number of data symbols by areceiving entity and a correction field that indicates whether or notthe calculated number of symbols should be corrected, and transmittingthe data packet.

Certain aspects of the present disclosure provide a computer-programproduct comprising a computer-readable medium having instructions storedthereon. The instructions are generally executable by one or moreprocessors for receiving a data packet comprising one or more datasymbols, extracting a length field and a correction field from the datapacket, and calculating a number of data symbols in the packet, based onthe length field and the correction field.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 illustrates a diagram of a wireless communications network inaccordance with certain aspects of the present disclosure.

FIG. 2 illustrates a block diagram of an example access point and userterminals in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates a block diagram of an example wireless device inaccordance with certain aspects of the present disclosure.

FIG. 4 illustrates an example structure of preamble transmitted from anaccess point in accordance with certain aspects of the presentdisclosure.

FIG. 5 illustrates example operations that may be performed at an accesspoint (AP) to provide a correction factor for an ambiguous length field,in accordance with certain aspects of the present disclosure.

FIG. 5A illustrates example means capable of performing the operationsshown in FIG. 5.

FIG. 6 illustrates example operations that may be performed at a userterminal to correct a number of data symbols calculated based on anambiguous length field, in accordance with certain aspects of thepresent disclosure.

FIG. 6A illustrates example means capable of performing the operationsshown in FIG. 6.

FIG. 7 illustrates an example of an ambiguous length field that may becorrected, in accordance with certain aspects of the present disclosure.

FIG. 8 illustrates an example of a correction field that may be providedto correct a number of data symbols calculated based on an ambiguouslength field, in accordance with certain aspects of the presentdisclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques that may be used tohelp resolve ambiguities in a data packet length field. The ambiguitiesmay arise when data symbols utilize short guard intervals (GIs). Datasymbols with these short GIs have a transmission time that is less thana resolution of a length field provided in the data packet, which mayresult in the same length field value being calculated for differentnumbers of symbols. The techniques provided herein may allow a receivingterminal to correct number of symbol calculations based on suchambiguous length field values.

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein one skilled in the art should appreciate that the scopeof the disclosure is intended to cover any aspect of the disclosuredisclosed herein, whether implemented independently of or combined withany other aspect of the disclosure. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof

An Example Wireless Communication System

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Spatial Division Multiple Access (SDMA),Time Division Multiple Access (TDMA), Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) systems, and so forth. An SDMA system mayutilize sufficiently different directions to simultaneously transmitdata belonging to multiple user terminals. A TDMA system may allowmultiple user terminals to share the same frequency channel by dividingthe transmission signal into different time slots, each time slot beingassigned to different user terminal An OFDMA system utilizes orthogonalfrequency division multiplexing (OFDM), which is a modulation techniquethat partitions the overall system bandwidth into multiple orthogonalsub-carriers. These sub-carriers may also be called tones, bins, etc.With OFDM, each sub-carrier may be independently modulated with data. AnSC-FDMA system may utilize interleaved FDMA (IFDMA) to transmit onsub-carriers that are distributed across the system bandwidth, localizedFDMA (LFDMA) to transmit on a block of adjacent sub-carriers, orenhanced FDMA (EFDMA) to transmit on multiple blocks of adjacentsub-carriers. In general, modulation symbols are sent in the frequencydomain with OFDM and in the time domain with SC-FDMA.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects, a wireless node implemented in accordance withthe teachings herein may comprise an access point or an access terminal

An access point (“AP”) may comprise, be implemented as, or known asNodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller(“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”),Transceiver Function (“TF”), Radio Router, Radio Transceiver, BasicService Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station(“RBS”), or some other terminology.

An access terminal (“AT”) may comprise, be implemented as, or known asan access terminal, a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a user terminal, a useragent, a user device, user equipment, a user station, or some otherterminology. In some implementations, an access terminal may comprise acellular telephone, a cordless telephone, a Session Initiation Protocol(“SIP”) phone, a wireless local loop (“WLL”) station, a personal digitalassistant (“PDA”), a handheld device having wireless connectioncapability, a Station (“STA”), or some other suitable processing deviceconnected to a wireless modem. Accordingly, one or more aspects taughtherein may be incorporated into a phone (e.g., a cellular phone or smartphone), a computer (e.g., a laptop), a portable communication device, aportable computing device (e.g., a personal data assistant), anentertainment device (e.g., a music or video device, or a satelliteradio), a global positioning system device, or any other suitable devicethat is configured to communicate via a wireless or wired medium. Insome aspects, the node is a wireless node. Such wireless node mayprovide, for example, connectivity for or to a network (e.g., a widearea network such as the Internet or a cellular network) via a wired orwireless communication link.

FIG. 1 illustrates a multiple-access multiple-input multiple-output(MIMO) system 100 with access points and user terminals. For simplicity,only one access point 110 is shown in FIG. 1. An access point isgenerally a fixed station that communicates with the user terminals andmay also be referred to as a base station or some other terminology. Auser terminal may be fixed or mobile and may also be referred to as amobile station, a wireless device or some other terminology. Accesspoint 110 may communicate with one or more user terminals 120 at anygiven moment on the downlink and uplink. The downlink (i.e., forwardlink) is the communication link from the access point to the userterminals, and the uplink (i.e., reverse link) is the communication linkfrom the user terminals to the access point. A user terminal may alsocommunicate peer-to-peer with another user terminal A system controller130 couples to and provides coordination and control for the accesspoints.

While portions of the following disclosure will describe user terminals120 capable of communicating via Spatial Division Multiple Access(SDMA), for certain aspects, the user terminals 120 may also includesome user terminals that do not support SDMA. Thus, for such aspects, anAP 110 may be configured to communicate with both SDMA and non-SDMA userterminals. This approach may conveniently allow older versions of userterminals (“legacy” stations) to remain deployed in an enterprise,extending their useful lifetime, while allowing newer SDMA userterminals to be introduced as deemed appropriate.

The system 100 employs multiple transmit and multiple receive antennasfor data transmission on the downlink and uplink. The access point 110is equipped with N_(ap) antennas and represents the multiple-input (MI)for downlink transmissions and the multiple-output (MO) for uplinktransmissions. A set of K selected user terminals 120 collectivelyrepresents the multiple-output for downlink transmissions and themultiple-input for uplink transmissions. For pure SDMA, it is desired tohave N_(ap)≧K≧1 if the data symbol streams for the K user terminals arenot multiplexed in code, frequency or time by some means. K may begreater than N_(ap) if the data symbol streams can be multiplexed usingTDMA technique, different code channels with CDMA, disjoint sets ofsubbands with OFDM, and so on. Each selected user terminal transmitsuser-specific data to and/or receives user-specific data from the accesspoint. In general, each selected user terminal may be equipped with oneor multiple antennas (i.e., N_(ut)≧1). The K selected user terminals canhave the same or different number of antennas.

The MIMO system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. The MIMO system 100may also utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported). The system 100 may also be a TDMA system if theuser terminals 120 share the same frequency channel by dividingtransmission/reception into different time slots, each time slot beingassigned to different user terminal 120.

FIG. 2 illustrates a block diagram of access point 110 and two userterminals 120 m and 120 x in the MIMO system 100. The access point 110is equipped with N_(t) antennas 224 a through 224 t. User terminal 120 mis equipped with N_(ut,m), antennas 252 ma through 252 mu, and userterminal 120 x is equipped with N_(ut,x) antennas 252 xa through 252 xu.The access point 110 is a transmitting entity for the downlink and areceiving entity for the uplink. Each user terminal 120 is atransmitting entity for the uplink and a receiving entity for thedownlink. As used herein, a “transmitting entity” is an independentlyoperated apparatus or device capable of transmitting data via a wirelesschannel, and a “receiving entity” is an independently operated apparatusor device capable of receiving data via a wireless channel. In thefollowing description, the subscript “dn” denotes the downlink, thesubscript “up” denotes the uplink, N_(up) user terminals are selectedfor simultaneous transmission on the uplink, N_(dn) user terminals areselected for simultaneous transmission on the downlink, N_(up) may ormay not be equal to N_(dn), and N_(up) and N_(dn) may be static valuesor can change for each scheduling interval. The beam-steering or someother spatial processing technique may be used at the access point anduser terminal

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. TX data processor 288processes (e.g., encodes, interleaves, and modulates) the traffic datafor the user terminal based on the coding and modulation schemesassociated with the rate selected for the user terminal and provides adata symbol stream. A TX spatial processor 290 performs spatialprocessing on the data symbol stream and provides N_(ut,m) transmitsymbol streams for the N_(ut,m) antennas. Each transmitter unit (TMTR)254 receives and processes (e.g., converts to analog, amplifies,filters, and frequency upconverts) a respective transmit symbol streamto generate an uplink signal. N_(ut,m) transmitter units 254 provideN_(ut,m) uplink signals for transmission from N_(ut,m) antennas 252 tothe access point.

N_(up) user terminals may be scheduled for simultaneous transmission onthe uplink. Each of these user terminals performs spatial processing onits data symbol stream and transmits its set of transmit symbol streamson the uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive theuplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(ap) received symbol streams from N_(ap)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing is performed in accordance withthe channel correlation matrix inversion (CCMI), minimum mean squareerror (MMSE), soft interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream is an estimate of adata symbol stream transmitted by a respective user terminal An RX dataprocessor 242 processes (e.g., demodulates, deinterleaves, and decodes)each recovered uplink data symbol stream in accordance with the rateused for that stream to obtain decoded data. The decoded data for eachuser terminal may be provided to a data sink 244 for storage and/or acontroller 230 for further processing.

On the downlink, at access point 110, a TX data processor 210 receivestraffic data from a data source 208 for N_(dn) user terminals scheduledfor downlink transmission, control data from a controller 230, andpossibly other data from a scheduler 234. The various types of data maybe sent on different transport channels. TX data processor 210 processes(e.g., encodes, interleaves, and modulates) the traffic data for eachuser terminal based on the rate selected for that user terminal TX dataprocessor 210 provides N_(dn) downlink data symbol streams for theN_(dn) user terminals. A TX spatial processor 220 performs spatialprocessing (such as a precoding or beamforming, as described in thepresent disclosure) on the N_(dn) downlink data symbol streams, andprovides N_(ap) transmit symbol streams for the N_(ap) antennas. Eachtransmitter unit 222 receives and processes a respective transmit symbolstream to generate a downlink signal. N_(ap) transmitter units 222providing N_(ap) downlink signals for transmission from N_(ap) antennas224 to the user terminals.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from access point 110. Each receiver unit 254 processesa received signal from an associated antenna 252 and provides a receivedsymbol stream. An RX spatial processor 260 performs receiver spatialprocessing on N_(ut,m) received symbol streams from N_(ut,m) receiverunits 254 and provides a recovered downlink data symbol stream for theuser terminal The receiver spatial processing is performed in accordancewith the CCMI, MMSE or some other technique. An RX data processor 270processes (e.g., demodulates, deinterleaves and decodes) the recovereddownlink data symbol stream to obtain decoded data for the user terminal

At each user terminal 120, a channel estimator 278 estimates thedownlink channel response and provides downlink channel estimates, whichmay include channel gain estimates, SNR estimates, noise variance and soon. Similarly, a channel estimator 228 estimates the uplink channelresponse and provides uplink channel estimates. Controller 280 for eachuser terminal typically derives the spatial filter matrix for the userterminal based on the downlink channel response matrix H_(dn,m) for thatuser terminal Controller 230 derives the spatial filter matrix for theaccess point based on the effective uplink channel response matrixH_(up,eff). Controller 280 for each user terminal may send feedbackinformation (e.g., the downlink and/or uplink eigenvectors, eigenvalues,SNR estimates, and so on) to the access point. Controllers 230 and 280also control the operation of various processing units at access point110 and user terminal 120, respectively.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within a wireless communication system,such as the MIMO system 100. The wireless device 302 is an example of adevice that may be configured to implement the various methods describedherein. The wireless device 302 may be an access point 110 or a userterminal 120.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 306. Theinstructions in the memory 306 may be executable to implement themethods described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A single or a plurality of transmit antennas 316 may be attached to thehousing 308 and electrically coupled to the transceiver 314. Thewireless device 302 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

FIG. 4 illustrates an example structure of a preamble 400 in accordancewith certain aspects of the present disclosure. The preamble 400 may betransmitted, for example, from the access point (AP) 110 to the userterminals 120 in the MIMO system 100 illustrated in FIG. 1.

The preamble 400 may comprise an omni-legacy portion 402 (i.e., thenon-beamformed portion) and a precoded IEEE 802.11ac VHT (Very HighThroughput) portion 404. The legacy portion 402 may comprise: a LegacyShort Training Field (L-STF) 406, a Legacy Long Training Field 408, aLegacy Signal (L-SIG) field 410, and two OFDM symbols for VHT Signal A(VHT-SIG-A) fields 412, 414. The VHT-SIG-A fields 412, 414 (i.e.,VHT-SIG-A1 and VHT-SIG-A2) may be transmitted omni-directionally and mayindicate allocation of numbers of spatial streams to a combination (set)of STAs.

The precoded IEEE 802.11ac VHT portion 404 may comprise a VHT ShortTraining Field (VHT-STF) 418, a VHT Long Training Field 1 (VHT-LTF1)420, VHT Long Training Fields (VHT-LTFs) 422, a VHT Signal B (VHT-SIG-B)field 424, and a data portion 426. The VHT-SIG-B field may comprise oneOFDM symbol and may be transmitted precoded/beamformed.

Robust MU-MIMO reception may involve the AP transmitting all VHT-LTFs422 to all supported STAs. The VHT-LTFs 422 may allow each STA toestimate a MIMO channel from all AP antennas to the STA's antennas. TheSTA may utilize the estimated channel to perform effective interferencenulling from MU-MIMO streams corresponding to other STAs. To performrobust interference cancellation, each STA may be expected to know whichspatial stream belongs to that STA, and which spatial streams belong toother users.

Guard Interval Signaling for Data Symbol Number Determination

The L-SIG field 410 may have a Length field that is indicates a packetduration as an integer number of symbols. For example, the L-SIG Lengthfield may indicate packet duration as an integer number of 4 us symbols.A receiving station may utilize the L-SIG Length field to determine thenumber of data symbols in a packet, in accordance with an equationdescribed in greater detail below.

In general, 802.11ac packets do not have a byte length field inVHT-SIG-A. Rather, the L-SIG LENGTH field contains a duration like in802.11n Mixed-Mode, which gives the packet duration as an integer numberof 4 microsecond (corresponding to 802.11a symbols). As a result, If ashort guard interval is used, there may be an ambiguity in the L-SIGLENGTH.

For example, different packets with x and x-1 symbols, may both have thesame L-SIG LENGTH. This ambiguity may only exist, however, for a numberof short guard interval symbols equal to 10n or 10n-1 where n is aninteger. The ambiguity is due to the nature of the equation used tocalculate the L-SIG LENGTH field, which includes a ceiling function. Aswill be described in greater detail below, for a data packet with 1VHT-LTF, data packets with 20 and 19 short GI symbols have the sameL-SIG LENGTH value.

However, as described above, ambiguities may arise when data symbolsutilize short guard intervals (GIs) with transmission times less than 4us, such as symbols with short GIs with transmission times of 3.6 us.Because, in this case, data packets with different numbers of symbols(N_(SYM)) may be transmitted with the same Length value, a receivingentity may determine an incorrect number of data symbols.

According to certain aspects, to allow a receiving entity to resolvethis ambiguity, a transmitting entity may transmit a field thatindicates a length of the GI used for data symbols and/or may alsoindicate whether or not a number of symbols calculated based on anambiguous Length field should be corrected.

As illustrated in FIG. 4, such a field may be transmitted in the form ofa multi-bit GI field 428. The GI field 428 may be included in theVHT-SIG-A field 412. As will be described in greater detail below, themulti-bit code of the GI field 428 may indicate whether a long or shortGI field is used in data symbols and, in the case of data symbols withshort GI, the GI field may also indicate whether the number of symbolscalculated based on the length field should be corrected.

FIG. 5 illustrates example operations that may be performed at an accesspoint (AP) to generate and provide a correction factor for an ambiguouslength field, in accordance with certain aspects of the presentdisclosure.

The operations 500 begin, at 502, by generating a data packet comprisingone or more data symbols. At 504, the AP provides, in a preamble fieldof the data packet, a length field that may be used to calculate anumber of symbols by a receiving entity, as well as an indication ofwhether or not the calculated number of symbols should be corrected. At506, the AP may transmit the data packet and a receiving entity maycalculate a number of data symbols based on the Length field and theindication.

FIG. 6 illustrates example operations 600 that may be performed, forexample, at a user terminal to correct a number of data symbolscalculated based on an ambiguous length field, in accordance withcertain aspects of the present disclosure.

The operations begin, at 602, by receiving a data packet comprising oneor more data symbols. At 604, the UT extracts a length field and acorrection field from the data packet. At 606, the UT calculates anumber of data symbols in the packet, based on the length field and thecorrection field.

FIG. 7 shows a table 700 of Length values for various packetconfigurations. The values illustrate the example, alluded to above, ofan ambiguous length field value for data packets with 20 and 19 short GIsymbols.

The values in the table 700 assume a data packet with 1 VHT-LTF. Asshown for long GI symbols, there is no ambiguity as each differentnumber of symbols (N_(SYM)), results in a different L-SIG LENGTH value.On the other hand, for short GI symbols, data packets with 20 and 19short GI symbols have the same L-SIG LENGTH value.

The reason for the ambiguity may be seen by examining the equation usedto calculate the length value:

LENGTH=ceil((TXTIME−20)/4)×3−3  (1)

where

TXTIME=36+4N _(VHT-LTF) +N _(SYM) T  (2)

where T is 4 or 3.6 microseconds depending on the guard interval (4 forlong, 3.6 for short), N_(SYM) is number of DATA symbols (does notinclude VHT-SIG-B), and 36+4N_(VHT-LTF) is duration of preamble inmicroseconds. This may include VHT-SIG-B which always uses a long guardinterval.

In the equation for L-SIG LENGTH, above, “ceil” is the ceiling function.Because “ceil(x)” is defined as “the smallest integer not less than x.”Because the argument of the ceiling function in the equation above has adivisor of 4 and, for short GI symbols, TXTIMEs for consecutive NSYMvalues will differ by less than four, the argument of the ceilingfunction will differ by less than one. Thus, in the event the argumentdoes not result in different integer values, the L-SIG LENGTH valueswill be the same, as with N_(SYM)=19 and 20.

FIG. 8 illustrates example values for a GI correction field that may beprovided to correct a number of data symbols calculated based on anambiguous length field, in accordance with certain aspects of thepresent disclosure. As discussed above, aspects of the presentdisclosure may help resolve this ambiguity by making the GI fielddescribed above dependent on the number of data symbols and, on thereceiver side, corresponding different equations may be used tocalculate N_(SYM), with the equation selected based on the GI bitvalues. While not shown, the value “b01” may be s reserved value.

While the LENGTH equation (1) above may be used most of the time, ifshort GI is used and the number of symbols modulo 10 is 9 (N_(SYM)%10=9), different equations may be used, to calculate N_(SYM). Forexample, for GI=b00, the following equation may be used (based on EQ (1)above):

N _(SYM)=ceil((LENGTH+3)/3)−4−N_(VHT-LTF)  (3)

for b10:

N_(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6)  (4)

and for b′11′

N _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6)−1  (5)

Thus, even if an ambiguous LENGTH value is transmitted, the ambiguitymay be resolved by using the correct N_(SYM) equation based on the GIfield.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering. For example, operations 500 and 600 illustrated inFIGS. 5 and 6 correspond to means 500A and 600A illustrated in FIGS. 5Aand 6A.

For example, means for transmitting may comprise a transmitter (e.g.,the transmitter unit 222) and/or an antenna 224 of the access point 110illustrated in FIG. 2. Means for receiving may comprise a receiver(e.g., the receiver unit 254) and/or an antenna 252 of the user terminal120 illustrated in FIG. 2. Means for processing, means for determining,or means for using may comprise a processing system, which may includeone or more processors, such as the RX data processor 270, the TX dataprocessor 288, and/or the controller 280 of the user terminal 120illustrated in FIG. 2.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining, and thelike. Also, “determining” may include receiving (e.g., receivinginformation), accessing (e.g., accessing data in a memory), and thelike. Also, “determining” may include resolving, selecting, choosing,establishing, and the like.

As used herein, a phrase referring to “at least one of a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM, and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof If implemented in hardware, anexample hardware configuration may comprise a processing system in awireless node. The processing system may be implemented with a busarchitecture. The bus may include any number of interconnecting busesand bridges depending on the specific application of the processingsystem and the overall design constraints. The bus may link togethervarious circuits including a processor, machine-readable media, and abus interface. The bus interface may be used to connect a networkadapter, among other things, to the processing system via the bus. Thenetwork adapter may be used to implement the signal processing functionsof the PHY layer. In the case of a user terminal 120 (see FIG. 1), auser interface (e.g., keypad, display, mouse, joystick, etc.) may alsobe connected to the bus. The bus may also link various other circuitssuch as timing sources, peripherals, voltage regulators, powermanagement circuits, and the like, which are well known in the art, andtherefore, will not be described any further.

The processor may be responsible for managing the bus and generalprocessing, including the execution of software stored on themachine-readable media. The processor may be implemented with one ormore general-purpose and/or special-purpose processors. Examples includemicroprocessors, microcontrollers, DSP processors, and other circuitrythat can execute software. Software shall be construed broadly to meaninstructions, data, or any combination thereof, whether referred to assoftware, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. Machine-readable media may include, by way ofexample, RAM (Random Access Memory), flash memory, ROM (Read OnlyMemory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof The machine-readable media may be embodied in acomputer-program product. The computer-program product may comprisepackaging materials.

In a hardware implementation, the machine-readable media may be part ofthe processing system separate from the processor. However, as thoseskilled in the art will readily appreciate, the machine-readable media,or any portion thereof, may be external to the processing system. By wayof example, the machine-readable media may include a transmission line,a carrier wave modulated by data, and/or a computer product separatefrom the wireless node, all which may be accessed by the processorthrough the bus interface. Alternatively, or in addition, themachine-readable media, or any portion thereof, may be integrated intothe processor, such as the case may be with cache and/or generalregister files.

The processing system may be configured as a general-purpose processingsystem with one or more microprocessors providing the processorfunctionality and external memory providing at least a portion of themachine-readable media, all linked together with other supportingcircuitry through an external bus architecture. Alternatively, theprocessing system may be implemented with an ASIC (Application SpecificIntegrated Circuit) with the processor, the bus interface, the userinterface in the case of an access terminal), supporting circuitry, andat least a portion of the machine-readable media integrated into asingle chip, or with one or more FPGAs (Field Programmable Gate Arrays),PLDs (Programmable Logic Devices), controllers, state machines, gatedlogic, discrete hardware components, or any other suitable circuitry, orany combination of circuits that can perform the various functionalitydescribed throughout this disclosure. Those skilled in the art willrecognize how best to implement the described functionality for theprocessing system depending on the particular application and theoverall design constraints imposed on the overall system.

The machine-readable media may comprise a number of software modules.The software modules include instructions that, when executed by theprocessor, cause the processing system to perform various functions. Thesoftware modules may include a transmission module and a receivingmodule. Each software module may reside in a single storage device or bedistributed across multiple storage devices. By way of example, asoftware module may be loaded into RAM from a hard drive when atriggering event occurs. During execution of the software module, theprocessor may load some of the instructions into cache to increaseaccess speed. One or more cache lines may then be loaded into a generalregister file for execution by the processor. When referring to thefunctionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer-readable medium.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a computer. By way of example,and not limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared (IR),radio, and microwave, then the coaxial cable, fiber optic cable, twistedpair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer- readable media (e.g., a signal). Combinations ofthe above should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

What is claimed is:
 1. A method for wireless communications, comprising:generating a data packet comprising one or more data symbols; providing,in a preamble field of the data packet, a length field used to calculatea number of data symbols by a receiving entity and a correction fieldthat indicates whether or not the calculated number of data symbolsshould be corrected, wherein the number of data symbols is based on thelength field and a number of training fields; and transmitting the datapacket.
 2. The method of claim 1, wherein the providing comprises:providing a first value for the correction field if a guard interval ofa first length is used and a first number of data symbols aretransmitted in the packet; and providing a second value for thecorrection field if the guard interval of a first length is used and asecond number of data symbols are transmitted in the packet.
 3. Themethod of claim 2, wherein: the first value is provided for thecorrection field if the number of data symbols modulo 10 is equal to 9;and the second value is provided otherwise.
 4. The method of claim 1,wherein the correction field comprises a 2-bit field.
 5. The method ofclaim 4, wherein the 2-bit field indicates whether the data symbols havea long or short guard interval.
 6. The method of claim 5, wherein a samevalue for the 2-bit field is used regardless of the number of datasymbols, if the data symbols have a long guard interval.
 7. The methodof claim 1, wherein the number of data symbols is represented by N_(SYM)and is calculated using one of expressions:N _(SYM)=ceil((LENGTH+3)/3)−4−N _(VHT-LTF);N_(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6); andN _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6)−1, whereinN_(VHT-LTF) is the number of Very High Throughput Long Training Fieldsand LENGTH is the length field, and wherein the expression is selectedbased on the correction field.
 8. The method of claim 1, wherein thetraining fields comprise Very High Throughput Long Training Fields(VHT-LTFs).
 9. A method for wireless communications, comprising:receiving a data packet comprising one or more data symbols; extractinga length field and a correction field from the data packet; andcalculating a number of data symbols in the packet, based on the lengthfield and a number of training fields.
 10. The method of claim 9,wherein: the correction field has a first value if a guard interval of afirst length is used and a first number of data symbols are transmittedin the packet; and the correction field has a second value if the guardinterval of a first length is used and a second number of data symbolsare transmitted in the packet.
 11. The method of claim 10, wherein: thefirst value is provided for the correction field if the number of datasymbols modulo 10 is equal to 9; and the second value is providedotherwise.
 12. The method of claim 9, wherein the correction fieldcomprises a 2-bit field.
 13. The method of claim 12, wherein the 2-bitfield indicates whether the data symbols have a long or short guardinterval.
 14. The method of claim 13, wherein a same value for the 2-bitfield is used regardless of the number of data symbols, if the datasymbols have a long guard interval.
 15. The method of claim 9, whereincalculating the number of data symbols in the packet, based on thelength field and the correction field, comprises selecting an equationfor use in calculating the number of data symbols, based on the value ofthe correction field.
 16. The method of claim 9, wherein the number ofdata symbols is represented by N_(SYM) and is calculated using one ofexpressions:N _(SYM)=ceil((LENGTH+3)/3)−4−N _(VHT-LTF);N _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6); andN _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6)−1, whereinN_(VHT-LTF) is the number of Very High Throughput Long Training Fieldsand LENGTH is the length field, and wherein the expression is selectedbased on the correction field.
 17. The method of claim 9, wherein thetraining fields comprise Very High Throughput Long Training Fields(VHT-LTFs).
 18. An apparatus for wireless communications, comprising:means for generating a data packet comprising one or more data symbols;means for providing, in a preamble field of the data packet, a lengthfield used to calculate a number of data symbols by a receiving entityand a correction field that indicates whether or not the calculatednumber of data symbols should be corrected, wherein the number of datasymbols is based on the length field and a number of training fields;and means for transmitting the data packet.
 19. The apparatus of claim18, wherein the means for providing comprises: means for providing afirst value for the correction field if a guard interval of a firstlength is used and a first number of data symbols are transmitted in thepacket; and means for providing a second value for the correction fieldif the guard interval of a first length is used and a second number ofdata symbols are transmitted in the packet.
 20. The apparatus of claim19, wherein: the first value is provided for the correction field if thenumber of data symbols modulo 10 is equal to 9; and the second value isprovided otherwise.
 21. The apparatus of claim 18, wherein thecorrection field comprises a 2-bit field.
 22. The apparatus of claim 21,wherein the 2-bit field indicates whether the data symbols have a longor short guard interval.
 23. The apparatus of claim 22, wherein a samevalue for the 2-bit field is used regardless of the number of datasymbols, if the data symbols have a long guard interval.
 24. Theapparatus of claim 18, wherein the number of data symbols is representedby N_(SYM) and is calculated using one of expressions:N _(SYM)=ceil((LENGTH+3)/3)−4−N _(VHT-LTF);N _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6); andN _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6)−1, whereinN_(VHT-LTF) is the number of Very High Throughput Long Training Fieldsand LENGTH is the length field, and wherein the expression is selectedbased on the correction field.
 25. The apparatus of claim 18, whereinthe training fields comprise Very High Throughput Long Training Fields(VHT-LTFs).
 26. An apparatus for wireless communications, comprising:means for receiving a data packet comprising one or more data symbols;means for extracting a length field and a correction field from the datapacket; and means for calculating a number of data symbols in thepacket, based on the length field and a number of training fields. 27.The apparatus of claim 26, wherein: the correction field has a firstvalue if a guard interval of a first length is used and a first numberof data symbols are transmitted in the packet; and the correction fieldhas a second value if the guard interval of a first length is used and asecond number of data symbols are transmitted in the packet.
 28. Theapparatus of claim 27, wherein: the first value is provided for thecorrection field if the number of data symbols modulo 10 is equal to 9;and the second value is provided otherwise.
 29. The apparatus of claim26, wherein the correction field comprises a 2-bit field.
 30. Theapparatus of claim 29, wherein the 2-bit field indicates whether thedata symbols have a long or short guard interval.
 31. The apparatus ofclaim 30, wherein a same value for the 2-bit field is used regardless ofthe number of data symbols, if the data symbols have a long guardinterval.
 32. The apparatus of claim 26, wherein calculating the numberof data symbols in the packet, based on the length field and thecorrection field, comprises selecting an equation for use in calculatingthe number of data symbols, based on the value of the correction field.33. The apparatus of claim 26, wherein the number of data symbols isrepresented by N_(SYM) and is calculated using one of expressions:N _(SYM)=ceil((LENGTH+3)/3)−4−N _(VHT-LTF);N _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6); andN _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6)−1, whereinN_(VHT-LTF) is the number of Very High Throughput Long Training Fieldsand LENGTH is the length field, and wherein the expression is selectedbased on the correction field.
 34. The apparatus of claim 26, whereinthe training fields comprise Very High Throughput Long Training Fields(VHT-LTFs).
 35. An apparatus for wireless communications, comprising: atleast one processor configured to: generate a data packet comprising oneor more data symbols, provide, in a preamble field of the data packet, alength field used to calculate a number of data symbols by a receivingentity and a correction field that indicates whether or not thecalculated number of data symbols should be corrected, wherein thenumber of data symbols is based on the length field and a number oftraining fields, and transmit the data packet; and a memory coupled withthe at least one processor.
 36. The apparatus of claim 35, wherein thenumber of data symbols is represented by N_(SYM) and is calculated usingone of expressions:N _(SYM)=ceil((LENGTH+3)/3)−4−N _(VHT-LTF);N _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6); andN _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6)−1, whereinN_(VHT-LTF) is the number of Very High Throughput Long Training Fieldsand LENGTH is the length field, and wherein the expression is selectedbased on the correction field.
 37. The apparatus of claim 35, whereinthe training fields comprise Very High Throughput Long Training Fields(VHT-LTFs).
 38. An apparatus for wireless communications, comprising: atleast one processor configured to receive a data packet comprising oneor more data symbols, extract a length field and a correction field fromthe data packet, and calculate a number of data symbols in the packet,based on the length field and a number of training fields; and a memorycoupled with the at least one processor.
 39. The apparatus of claim 38,wherein the number of data symbols is represented by N_(SYM) and iscalculated using one of expressions:N _(SYM)=ceil((LENGTH+3)/3)−4−N _(VHT-LTF);N _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6); andN _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6)−1, whereinN_(VHT-LTF) is the number of Very High Throughput Long Training Fieldsand LENGTH is the length field, and wherein the expression is selectedbased on the correction field.
 40. The apparatus of claim 38, whereinthe training fields comprise Very High Throughput Long Training Fields(VHT-LTFs).
 41. A computer-program product comprising a non-transitorycomputer-readable medium having instructions stored thereon, theinstructions executable by one or more processors for: generating a datapacket comprising one or more data symbols; providing, in a preamblefield of the data packet, a length field used to calculate a number ofdata symbols by a receiving entity and a correction field that indicateswhether or not the calculated number of data symbols should becorrected, wherein the number of data symbols is based on the lengthfield and a number of training fields; and transmitting the data packet.42. The computer program of claim 41, wherein the number of data symbolsis represented by N_(SYM) and is calculated using one of expressions:N _(SYM)=ceil((LENGTH+3)/3)−4−N _(VHT-LTF);N _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6); andN _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6)−1, whereinN_(VHT-LTF) is the number of Very High Throughput Long Training Fieldsand LENGTH is the length field, and wherein the expression is selectedbased on the correction field.
 43. The computer program of claim 41,wherein the training fields comprise Very High Throughput Long TrainingFields (VHT-LTFs).
 44. A computer-program product comprising anon-transitory computer-readable medium having instructions storedthereon, the instructions executable by one or more processors for:receiving a data packet comprising one or more data symbols; extractinga length field and a correction field from the data packet; andcalculating a number of data symbols in the packet, based on the lengthfield and a number of training fields.
 45. The computer program of claim44, wherein the number of data symbols is represented by N_(SYM) and iscalculated using one of expressions:N _(SYM)=ceil((LENGTH+3)/3)−4−N _(VHT-LTF);N _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6); andN _(SYM)=floor((ceil((LENGTH+3)/3)−4−N_(VHT-LTF))*4/3.6)−1, whereinN_(VHT-LTF) is the number of Very High Throughput Long Training Fieldsand LENGTH is the length field, and wherein the expression is selectedbased on the correction field.
 46. The computer program of claim 44,wherein the training fields comprise Very High Throughput Long TrainingFields (VHT-LTFs).